The present invention is directed to integrated circuits and their processing for the manufacture of semiconductor devices. More particularly, the invention provides a method and a device for an oxidation process for the manufacture of integrated circuits. Merely by way of example, the invention has been applied to techniques related to forming gate dielectric of transistor. But it would be recognized that the invention has a much broader range of applicability.
Integrated circuits or “ICs” have evolved from a handful of interconnected devices fabricated on a single chip of silicon to millions of devices. Current ICs provide performance and complexity far beyond what was originally imagined. In order to achieve improvements in complexity and circuit density (i.e., the number of devices capable of being packed onto a given chip area), the size of the smallest device feature, also known as the device “geometry”, has become smaller with each generation of ICs. Semiconductor devices are now being fabricated with features less than a quarter of a micron across.
One of the fabrication processes of ICs is oxidation, which forms insulating layers. For example, silicon oxide grows on a silicon wafer to form dielectrics by exposing the silicon wafer to O2 at high temperatures, between 700 and 1100° C. in a furnace. It may use either water vapor (steam) or molecular oxygen as the oxidant; it is consequently called either wet or dry oxidation. During a thermal oxidation process, silicon atoms on the clean Si wafer surface react with either molecular oxygen or water vapor to form SiO2. Thermal oxide incorporates silicon from the substrate and combines with oxygen supplied from the ambient. Thus, it grows both down into the wafer and extends out of the silicon surface. For every unit thickness of silicon consumed, 2.17 unit thicknesses of silicon oxide will be formed. If a bare silicon surface is oxidized, 46% of the oxide thickness will lie below the original surface, and 54% above it.
Wet oxidation process provides a faster growth rate for silicon oxide than a dry oxidation for growing a thick thermal oxide. Typically, a dry oxidation process, though a wet oxidation process is not excluded, is used for producing high quality silicon oxide films with a thin or ultra-thin thickness. Over the past, dry oxidation techniques have been employed to form thin dielectric layer for a gate structure of a metal-oxide-semiconductor field-effect-transistor (MOSFET). For example, a layer of SiO2 is formed as dielectric between the electrical contact and the underlying substrate.
FIG. 1 is a conventional MOSFET structure 100. MOSFET structure 100 includes a substrate 101. Within the substrate, a gate region 106 is positioned between a source region 103 and a drain region 102. A gate structure 105 overlies the gate region 106. Typically, gate structure 105 includes electrical conductive materials, such as polysilicon, silicide, etc. A gate dielectric layer 104 is formed between the gate structure 105 and the substrate.
In order to reduce sizes of integrated circuits, it is often necessary to reduce the thickness of dielectric layer 104. Over the past, various conventional techniques have been developed for forming gate dielectric. Unfortunately, conventional techniques are often inadequate.
Therefore, it is desired to have an improved method for forming gate structures, including the gate dielectric.